Can't gain weight, fat or muscle mass, need mass building advise and twenkies don't count.

BLUEPine
I am 5 11' and 120 lb. and can't gain weight, I eat anything I want whenever I want and eat tons of Ice cream, and I am 35 lb. under the recommended weight.

For the past month I have been working out for 30 min a day alternating between upper, mid, and lower workouts with 3 reaps for each lift, and have made little progress in increasing the weight I can lift. As well I have lost 3 pounds (was at 123 lb) I have not gained any muscle and am concerned about continuing my workout because It will be bad for my body if I loss more weight.

I need advice on ways to gain weight preferably muscle mass without supplements. Also any affective workouts? Thanks
Can't gain weight, fat or muscle mass, need mass building advise and twenkies don't count.
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